A central problem in developmental neurobiology is to understand the molecular mechanisms that regulate neuronal differentiation. Expanding our knowledge of these molecular mechanisms will not only give us insight into developmental mechanisms but also lend insight into neurological disorders characterized by defects in CNS development. To gain insight into the molecular mechanisms that specify multiple aspects of cell fate, neuronal differentiation, and axonal and dendritic morphologies, I propose to examine the role of Notch signaling in cortical development and identify the molecular mechanisms by which it influences neuronal differentiation. To accomplish this goal I will first characterize and determine the subcellular localization of Notch protein in neurons of the developing cerebral cortex in vivo and in vitro using immunochemical techniques and confocal microscopy. Secondly, I will use mammalian homologues of the Drosophila Notch interacting proteins, Numb and Su(H), in gene transactivation and immunoprecipitation experiments to begin to identify the molecular mechanisms involved in Notch mediated gene activation in mammalian cortical neurons. Finally, I will examine the functional consequences of Notch mediated signaling on axonal and dendritic differentiation by altering Notch signaling with transfection and antisense oligonucleotide techniques in dissociated cortical neuron cultures and in cortical slice cultures. These experiments should significantly advance our understanding of the role of Notch signaling in mammalian neural development.